This relates generally to imaging devices, and more particularly, to imaging devices having image sensor pixels with charge storage capabilities.
Image sensors are commonly used in electronic devices such as cellular telephones, cameras, and computers to capture images. In a typical arrangement, an electronic device is provided with an array of image pixels arranged in pixel rows and pixel columns. Circuitry is commonly coupled to each pixel column for reading out image signals from the image pixels.
The image pixels contain a photodiode for generating charge in response to image light and a corresponding charge storage region. The photodiode and charge storage region are formed within a semiconductor substrate. Image sensors are often configured to operate using a global shutter or a rolling shutter scheme. When operating under a global shutter scheme, all of the pixels in the image sensor are reset simultaneously. A charge transfer operation is then used to simultaneously transfer the charge collected in the photodiode of each image pixel to the associated charge storage region. Data from each charge storage region is then read out on a per-row basis. When operating under a rolling shutter scheme, all of the pixels in a row in the image sensor are reset simultaneously. A charge transfer operation is used to transfer charge from the photodiodes to associated charge storage regions row-by-row. The charge storage regions are then read out row-by-row after some integration time between shutter and readout.
In conventional image sensor pixels, the charge storage region occupies a substantially similar sized area on the semiconductor substrate as the photodiode. However, occupying excessive area on the semiconductor substrate can undesirably expose the charge storage region to light that reduces the shutter efficiency of the image system. Additionally, excessively large charge storage regions reduce the size of the corresponding photodiode and thus the overall sensitivity of the pixel.
It would therefore be desirable to be able to provide imaging devices with improved image sensor pixels.